Among those who learned that robbing the U.S. mail leads to trouble was William Patrick Colbeck. Through the mid 1920s, Colbeck was part of an organized crime operation in Illinois, focusing on smuggling liquor during prohibition.

Although suspected of committing murders and several other robberies, it was the mail robbery that brought Colbeck to justice. Colbeck went after mining company payroll cash that was being moved by mail. In November 1924 he and five associates were convicted of mail robbery and sentenced to fifteen years in prison. This cartoon, published in the St. Louis Star, notes that criminals would do well to avoid trying to attack the U.S. mail.

Postal inspectors began their work when Postmaster General Benjamin Franklin named William Goddard surveyor of the post in 1776. Through the nineteenth century, their roles evolved beyond their primary duty to ensure the successful transportation of mail. By the mid 1800s, inspectors were playing an active role in criminal investigations and law enforcement.

As mail volume grew, so did the number of unscrupulous individuals who tried to steal the mail or use it for illegal or harmful purposes. When swindlers used the growing mail system to target people after the Civil War, inspectors added mail fraud investigations to their duties.